Vesicular release of neurotransmitters, the process of exocytosis, impacts many functional aspects of the nervous system. Changes in neurotransmitter release are implicated in drug abuse, diseases (e.g. Parkinson's, Alzheimer's), aging and memory loss. Significant progress has been made in understanding exocytosis via electrochemical studies of neurotransmitters via microelectrodes. However, current techniques are limited to a spatial resolution of approximately a micron, making it difficult to study neurotransmitter dynamics near and within the synapse. In order to study exocytosis with significantly improved spatial resolution recording and measurement, methods and instruments with nanometer resolution are needed. In addition, it has been difficult to study non-electrochemically active neurotransmitters (e.g., acetylcholine) using traditional sensors. Here we propose to develop electrochemical sensor that will enable us to interrogate exocytosis with a nanometer resolution. A key objective is qualitative and quantitative measurement of neurotransmitter release and uptake within model synapses of Aplysia californica neurons with both appropriate electrical (action potentials) and chemical stimuli (e.g. K+, Ca2+). The novel nanosensor allows the detection of both electrochemical active and non-active neurotransmitters. Our armamentarium includes novel nanopositioning, imaging and measurement systems based on scanning electrochemical microscope. These tightly coupled technology development and neuroscience efforts will resolve issues related to neurotransmitter identity, concentration, and the conditions needed for transmitter release with nanometer spatial resolution, improved signal to noise ratio, and high temporal resolution. These efforts are well matched to the goal of PA-11-149, Nanoscience and Nanotechnology in Biology and Medicine. The approaches are general and adaptable to a range of neuronal cells. The resulting new toolset and new knowledge about neurotransmission will be transferrable to broader research community and will have a high impact on the neurochemical research.